Ice Detection

CHAPTER 11

ICE DETECTION

The ANO Schedule 4 states that:

In the case of an aircraft of MTWA exceeding 5700 kg (12500 lb), means of observing the existence and build up of ice on the aircraft must be provided.

The equipment will be carried on flights when the weather reports or forecasts available at the aerodrome at the time of departure indicate that conditions favouring ice formation are likely to be met.

Serrated Rotor Ice Detector Head

Serrated Rotor Ice Detector

Figure 4

This consists of a serrated rotor, incorporating an integral drive shaft coupled to a small ac motor via a reduction gearbox, being rotated adjacent to a fixed knife-edge cutter. The motor casing is connected via a spring-tensioned toggle bar to a micro-switch assembly. The motor and gearbox assembly is mounted on a static spigot attached to the motor housing and, together with the micro-switch assembly, is enclosed by a cylindrical housing. The detector is mounted through the fuselage side so that the inner housing is subjected to the ambient conditions with the outer being sealed from the aircraft cabin pressure.The serrated rotor on the detector head is continuously driven by the electrical motor so that its periphery rotates within 0.050 mm (0.002 in) of the leading edge of the knife-edge cutter. The torque therefore required to drive the rotor under non-icing conditions will be slight, since bearing friction only has to be overcome. Under icing conditions, however, ice will accrete on the rotor until the gap between the rotor and knife-edge is filled, whereupon a cutting action by the knife edge will produce a substantial increase in the required torque causing the toggle bar to move against its spring mounting and so operate the microswitch, to initiate a warning signal....